Who cares what the sharpest aperture is, really? Do you change aperture because of sharpness? Sharpness of what? I use aperture to control my DOF or flash exposure. If my lens is sharpest at f/4, I don't care because how does that have any real useful impact on your photography?

Second reason I don't care is because just because my lens is sharpest at f/4, doesn't mean it's NOT sharp at other apertures. So again, I don't care.

Sure I do. I shoot a lot of very high detail subjects (birds...loads and loads of fine detail). For me, its imperative to get as much light down the lens as possible while maximizing sharpness, and flash is rarely an option (more so because it takes too long to recharge, and I often have to fire off a string shots at 8fps to get a single keeper). Less light means more noise, more noise means more NR, more NR means less, often considerably less, fine detail. If I was using a sensor with larger pixels, the sharpness issue would be largely moot, since the pixel pitch would intrinsically limit maximum resolution anyway. I use a Canon 7D, however, which is about 1.6 times as dense as the 1D X or 1.45 times as dense as the 5D III. Those two max out at 72 and 80 lp/mm, respectively and can't resolve any more detail than you get at an f/8 aperture anyway. The 7D has a theoretical peak resolution of 116 lp/mm, allowing it to resolve most of the detail you can get from f/5.6. As such, I try to shoot around f/5.6 or slightly wider (which helps improve image crispness...or microcontrast...if the lens can resolve more detail than the sensor). I've found that f/4 is a great aperture for small passerines (song/perching birds)...gets me just enough DOF to capture an entire bird, maximizes light down the lens, nicely blurs out backgrounds...in other words, it maximizes the quality of my work. There IS an impact.

If f/8 offers you the same benefit, great! More power to you. But there isn't any need to go around dissing those of us who prefer to KNOW the technological capabilities of our gear so we can maximize the potential of our own work. Not everyone requires the use of f/8 to attain a deeper DOF.

3rd gear in a Porsche will get you there, but to maximize your vehicle's potential, you have to get to the higher gears.

Sharpness is the ONLY route of maximizing potential? Secondly, nobody was dissing anyone. That's great if you know where your lens is sharpest for what you do and you can use that information to get photos you want, sure. Personally and for my work, it doesn't matter. I'm not going for the absolute sharpest shots I can possibly take, I'm going for the shots with the correct amount of lighting and correct amount of DOF. Sharpness is not a "higher gear." If I'm shooting portrait shots and want a great amount of bokeh, and my lens is sharpest at f/5.6, and I shoot there because it's sharpest there, I will be fired very quickly. That is why I personally don't need to know where it is sharpest. I just don't.

Thats great...for you. However, remember the original question was asking what aperture offered the best sharpness. I believe you were the first to answer with the canned "f/8 is best for all my lenses". Not only was that information anecdotal, its simply wrong...and the fact that it was wrong is why your getting flak. In light of the original question asked by @jdramirez, it doesn't really matter that f/8 is great "for you". The correct answer is that the maximum sharpness of a lens tends to be around 1 stop or so down from maximum aperture, and closer as lens build and glass quality goes up. For most lenses with normal aperturs...f/2.8-f/5.6, the "sweet spot" tends to fall around f/4.5 on average. For fast lenses, that sweet spot tends to fall around f/2.8 or so. At those apertures, a high resolution sensor (think Canon 18mp, Sony Exmor 36.3mp FF pr 24.2mp APS-C) is capable of resolving considerably more detail than is possible at f/8 (were talking some 240+ lp/mm at f/2.8, vs about 85 lp/mm at f/8).

Particularly in the case of macro photography, where the use of focus stacking is an option, an f/4 aperture could be used on the Canon EF 100mm f/2.8 Macro lens to maximize sharpness and get as much DOF as you want. Technically speaking, there is no reason you couldn't use a similar technique, such as the Brenizer Method, with the 70-200 to achieve a similar effect, mazimizing both sharpness and bokeh, for portraiture.

Great, f/8 works for you...but its the wrong answer, factually and technically incorrect. For the sake of the OP, I think its important thats pointed out. Obviously, the artistic needs of the job reign supreme...if you need DOF or you need creamy bokeh, then do what you need to do. But if your goal is to maximize sharpness, having the knowledge to do so is valuable, regardless of what works for you personally.

It was pointed out again, and again, and again, and again, and again..........

I just still don't understand what it even means though. The depth of field changes for each aperture. How can one aperture be "sharper" than another? At f/1.4, my background isn't sharp. What exactly are we talking about anyways? I can understand a portrait shot, say at f/1.8, vs. f/2.8. Is that what we mean? The face is sharper at 2.8? Shooting at the same focal plane? On the other hand, at f/11, my whole scene is sharp. It just doesn't make a whole lot of practical sense to me, unless we're talking a flat surface focal plane, at the same distance.

It was pointed out again, and again, and again, and again, and again..........

I just still don't understand what it even means though. The depth of field changes for each aperture. How can one aperture be "sharper" than another? At f/1.4, my background isn't sharp. What exactly are we talking about anyways? I can understand a portrait shot, say at f/1.8, vs. f/2.8. Is that what we mean? The face is sharper at 2.8? Shooting at the same focal plane? On the other hand, at f/11, my whole scene is sharp. It just doesn't make a whole lot of practical sense to me, unless we're talking a flat surface focal plane, at the same distance.

Assuming a "perfect" lens (one in which zero optical aberrations are present...that is CA, spherical aberration, field curvature, etc.), the only thing that limits resolution (which is the objective measure of acutance and microcontrast) is diffraction. As your aperture gets wider, the effects of diffraction become less and less. Sharpness (in the context I believe you are using) is a somewhat subjective measure of acutance and microcontrast...how harsh edges appear, how fine detail is discerned...and as such sharpness improves as resolution improves. Higher resolution also allows you to resolve finer details, and resolve larger details more sharply, vs. only being able to resolve larger details. At f/22, your limited, by diffraction, to only 30 lp/mm. If the detail you are interested in is larger than 30 lp/mm, your lens will resolve them, and the larger the detail the more clearly it will be resolved. At f/8 resolution jumps to 85 lp/mm, allowing you to resolve detail less than half the size as what you could resolve at f/22. By f/2.8, resolution increases to 245 lp/mm...again allowing you to resolve more fine detail, nearly 3x more detail than you could resolve at f/8.

In the case of, say, a macro subject (such as an insect), or a bird, or furry animal...there is PLENTY of very fine detail. If we use birds as an example, every feather has a shaft, on either side of which is a vane, each vane of which contains barbs, and each barb of which contains interlocking barbules, each barbule containing multiple fine hooks that assist in that interlocking. At f/8 and a shooting distance comfortable to most birds, I can resolve a vane and its barbs, but the fine barbule detail is blurred away. The shaft and each barb may be sharp relative to each other, however there is a considerable amount of detail that can't be resolved at all at this resolution, or if it is, its rather blurry. At a bird-comfortable shooting distance, barbule detail can be over 100 lp/mm. At f/4, my resolving power increases to around 170 lp/mm, allowing me to resolve much more of that fine barbule detail than I could at f/8 (only limited by sensor resolution...which is where high res. APS-C sensors like Canon's 116 lp/mm (luminance) 18mp sensor or Sony's 129 lp/mm (luminance) 24mp sensor). Now, not only are the spine and barbs sharp...they are sharper than they would have been at f/8 due to the improved acutance and microcontrast offered by a wider diffraction-limited aperture, and a finer level of detail is now resolving, adding even more to the impression of overall image sharpness.

The same rough effect would exhibit for any kind of photography that aims to expose fine detail. Insect macro photography definitely benefits, as insects contain even more fine detail than birds. When it comes to macro photography, due to extension, your effective aperture is often much smaller than indicated by your F-Number (in the case of the Canon MP-E 65mm Macro, at full extension the effective aperture can be f/96 or greater if you really stop down to maximize DOF.) Its for this very reason that focus stacking has become a popular mechanism for maximizing DOF and sharpness in macro photos...you can NEVER resolve as much fine detail as sharply at an effective f/96 as you can at say an effective f/22...diffraction simply won't allow it.) The same general rules would apply to portraiture as well...not quite as much fine detail, but still plenty to think about. Sharpness in hair, eye lashes, even iris detail (if your doing head shots) can all benefit from improved resolution at wider apertures...assuming other artistic goals don't override sharpness (which entirely depends on your style.) Many heat shot photographers resort to intriguing post-processing techniques to improve eye detail (many of which produce great results)...but there is no real substitute to finely resolved real, natural iris detail that you can achieve at f/5.6 on a high res (say D800) sensor IMHO.

One aperture can be sharper than another when it increases acutance and microcontrast, and when it resolves finer detail than another clearly...for the depth of field that is in focus (which, admittedly, may be very thin...but thats beside the point when talking purely about resolution...about sharpness.)

I see your point. It is clear. I guess I just wasn't thinking that way when I read the original question. I was thinking about working with a landscape or architecture photographer and me telling him I'm going to shoot at f/2 because that's the sharpest aperture for the lens, and then him taking my camera and lens away from me. I can agree that at a fixed focal length, and consistent, fixed focal plane, a lens can be sharper at f/2 vs. f/8, or what have you. I also interpreted as, ok, what aperture will make most of my scene sharpest? I guess there are several ways to think about and measure sharpness. I suppose if you picked a finite point in the landscape scene, let's say your focal point you chose, and shot at f/4 and then f/11, sure the whole scene would be in focus at f/11, but perhaps that point you focused on is sharper at f/4, than f/11.

I see your point. It is clear. I guess I just wasn't thinking that way when I read the original question. I was thinking about working with a landscape or architecture photographer and me telling him I'm going to shoot at f/2 because that's the sharpest aperture for the lens, and then him taking my camera and lens away from me. I can agree that at a fixed focal length, and consistent, fixed focal plane, a lens can be sharper at f/2 vs. f/8, or what have you. I also interpreted as, ok, what aperture will make most of my scene sharpest? I guess there are several ways to think about and measure sharpness. I suppose if you picked a finite point in the landscape scene, let's say your focal point you chose, and shot at f/4 and then f/11, sure the whole scene would be in focus at f/11, but perhaps that point you focused on is sharper at f/4, than f/11.

Aye, the artistic needs should certainly outweigh achieving maximum sharpness. When it comes to landscapes, I'd pick f/11 on any normal lens, or I'd use a tilt/shift lens and use tilt to maximize focus to infinity at a more ideal aperture like f/4 or f/5.6. For architecture, its roughly the same deal...not much in the way of very fine detail in architecture, and you could probably stop down to your hearts content if you wanted to. For portraiture, if you need to get your full subject within DOF, f/8 is certainly going to do a better job making your entire subject sharp vs. f/4. Even if it limits the amount of fine detail that can be resolved, using a wider aperture would be antithetical to your primary goals.

I see your point. It is clear. I guess I just wasn't thinking that way when I read the original question. I was thinking about working with a landscape or architecture photographer and me telling him I'm going to shoot at f/2 because that's the sharpest aperture for the lens, and then him taking my camera and lens away from me. I can agree that at a fixed focal length, and consistent, fixed focal plane, a lens can be sharper at f/2 vs. f/8, or what have you. I also interpreted as, ok, what aperture will make most of my scene sharpest? I guess there are several ways to think about and measure sharpness. I suppose if you picked a finite point in the landscape scene, let's say your focal point you chose, and shot at f/4 and then f/11, sure the whole scene would be in focus at f/11, but perhaps that point you focused on is sharper at f/4, than f/11.

Aye, the artistic needs should certainly outweigh achieving maximum sharpness. When it comes to landscapes, I'd pick f/11 on any normal lens, or I'd use a tilt/shift lens and use tilt to maximize focus to infinity at a more ideal aperture like f/4 or f/5.6. For architecture, its roughly the same deal...not much in the way of very fine detail in architecture, and you could probably stop down to your hearts content if you wanted to. For portraiture, if you need to get your full subject within DOF, f/8 is certainly going to do a better job making your entire subject sharp vs. f/4. Even if it limits the amount of fine detail that can be resolved, using a wider aperture would be antithetical to your primary goals.

This thread makes me sad. Why are you people running so many tests with your lenses to determine absurd things like sharpness? What does that even mean? And what is the point of it?

Why does it bother you?Why wouldn't someone want to understand and know how best to use their tools. Certainly there is a lot more than sharpness, but, if you do not understand your tools, then you are just taking what comes at random.

I bought two lenses and I prefer to take most of my shots near or on the mythical sweetspot in regards to aperture. With the presumption of sufficient light, for my 50mm f/1.4 I try to stay between 2.8 and 4.0. For my 24-105mm f/4 I make an effort to approach f/8, but that isn't always an option.

So that raises the aforementioned question. What aperture range is the 100mm and the 70-200 the sharpest? And don't hesitate to tell me that I was wrong about the 50 and 24-105... if indeed I'm way off.

The lens is sharp all the way through, from 2.8 through f/11... then it starts to hit the other side of the bell curve.

I really love the lens... it is my favorite over my 50mm f/1.4, 24-105, and 8mm fisheye (but that is completely different). I did just get a 70-200mm f/2.8L IS mkii today... so it is possible that will become my new favorite. I was looking at the DP and comparing the two lenses, and the 70-200 is supposed to be nearly as sharp as my 100mm. I guess the proof will be in the pudding.